1. Field of the Invention
The present invention relates to optical pickup apparatuses employed for the optical disk drive, in particular, an optical pickup apparatus capable of constructing an optical systems nearly identifying the optical path of illuminating light rays and the other optical path of detecting light rays by use of a light rays flux separating element consisting of birefringent (complex refraction) crystal, another optical pickup apparatus which is small-sized and has a small number of employed parts, and still another optical pickup apparatus executing information record and reproduction and further executing focus servo and tracking servo.
2. Description of the Related Art
Concerning the documents respectively describing the technologies in relation to the first group of the present invention, there exist some documents as listed up below:
1) Japanese Laid-open Patent Publication No. 56-61043/1981 “A FOCUS DETECTING APPARATUS”,
2) Japanese Laid-open Patent Publication No. 4-87041/1992 “AN OPTICAL DETECTOR”,
and
3) Japanese Laid-open Patent publication No. 5-120755/1993, “AN OPTICAL HEAD”.
The above-listed document 1) relates to a focus detecting apparatus and describes that, in an information reading-out apparatus which focuses the light rays spot through the objective lens onto the information track of the recording medium having the information recorded thereon spirally or in a state of concentric circles and reads out the information therefrom, the above-mentioned focus detecting apparatus detects whether the light rays spot is correctly focused by the objective lens onto the recording medium.
The document further describes that a prism made of a birefringent material such as Rochon prism is disposed between the coupling lens (CL) and the objective lens, there reflection light rays reflected on the disk are separated from the incident light rays, the light rays flux thus separated causes an astigmatism in order to obliquely enter the coupling lens as the incident light rays, and thereby the focus detection is performed.
And further, the other above-listed
document 2) describes that, in order to simplify the construction of the optical pickup apparatus for reading out the information signal written in the magneto-optic disk and in order to facilitate the assembling and manufacturing processes thereof, an inclined uniaxial crystal plate is mounted on the supporter of the light-receiving element, and thus a detection system for detecting the magneto-optic signal, the focus signal and the track signal is constructed, for the purpose of simplifying the detection system.
Furthermore, the still other above-listed
document 3) describes the optical pickup apparatus in which, in order to enable to detect the focus error signal always with high precision and in order to detect the magneto-optic signal at the same time, the semiconductor laser (LD) employing hologram and the light detector (PD) are unitarily constructed.
FIG. 11 is a configuration diagram showing the construction of the first example of the conventional optical pickup device.
In FIG. 11, the reference numeral 21 represents a semiconductor laser (LD), 22 a coupling lens (CL), 23 a polarized light beam splitter (PBS), 24 a deflecting mirror, 25 a quarter-wave (λ/4) plate, 26 an objective lens, 27 a recording medium, 28 a detecting lens (DL), 29 a cylinder lens, 30 a four-divisional light receiving element (PD), and 31 a detection system.
The linearly-polarized divergent light rays emitted from the semiconductor laser (LD) 21 are converted to the parallel light rays by the coupling lens 22, pass through the polarized light beam splitter (PBS) 23, and are deflected by the deflecting mirror 24.
The deflected light rays are further converted to the circularly-polarized light rays by the quarter-wave (λ/4) plate 25 and focused on the recording surface of the light recording medium 27 by the objective lens 26. The light rays flux reflected on the recording surface is made again parallel by the objective lens 26 and further converted to the linearly-polarized light rays in which the polarizing surface thereof is relatively rotated by 90° to the incident light rays. The light rays thus converted pass through the deflecting mirror 24, and the same are reflected on the PBS 23 and guided to the detection system 31. The light rays flux guided to the detection system 31 passes through the detecting lends 28 and the cylinder lens 29, and is detected by the four-divisional light-receiving element 30. On this occasion, the focus error signal is obtained by the astigmatism, the track error signal is obtained by the push-pull method, and the Rf signal is obtained by the variation of the four-divisional summed light amount (light intensity), that is, the difference of the reflection rate from the disk.
Conventionally, as mentioned heretofore, there exists some extent of limitation in small-sizing the optical system, in order to completely separating the optical path of the illuminating light rays and that of the detecting light rays by use of the PBS (polarized light beam splitter).
And further, although it has been already proposed to separate the light rays flux by utilizing the hologram, there existed some problems to be solved in the efficiency of utilizing the light rays.
Concerning the documents respectively describing the prior-art technologies in relation to the second group of the present invention, there exist some documents as listed up below;
1) Japanese Laid-open Patent Publication No. 4-87041/1992 “Light Detector”,
2) Japanese Laid-open Patent Publication No. 4-155629/1992 “Optical Pickup”
and
3) “Hologram Pickup for use in Laser Disk” (Edited by Sachio Kurata and other seven members, SHARP Technical Report Vol. 48, March 1991, P. 21-26).
The above-listed
document 1) describes that a uniaxial crystal board is mounted on the supporter for supporting a light detecting element having plural light-receiving surfaces so as to slantedly oppose to the respective light-receiving surfaces of the above light detecting element, and thereby the construction of the optical pickup device can be simplified, namely, the light-receiving element and the light detecting optical element is unitarily combined into one.
Furthermore, the above-listed
document 2) describes that the optical pickup comprises a lens member having the light-emitting element and the light-receiving element both hermetically enclosed (sealed) therein and further having a lens surface formed on one end thereof for focusing the outgoing light rays emitted from the light emitting element, and biaxial driving means for positioning the above-mentioned lens member in both of the focus direction and the radius direction of the optical disk, and further, a hologram for guiding a part of the outgoing light rays of the light-emitting element reflected on the optical disk toward the light receiving element is formed on the lens surface of the afore-mentioned lens member, so that an optical pickup can be constructed with small number of employed parts and the reproduced signal does not vary due to the time-elapsing variation by stabilizing the positional relationship between the light-emitting element and the light-receiving element. Namely, in the document 2), the light rays flux is separated into two, one for the semiconductor laser and another one for the light-receiving element by use of the hologram, and the semiconductor laser and the light-receiving element are unitarily combined into one.
Furthermore, the above-listed
document 3) describes a hologram pickup, in which plural functions for use in CD are integrated in one hologram element, and a laser diode employed as a light source and a photo diode for detecting the signal are disposed in one package.
FIG. 16 is a construction diagram for illustrating the construction of the second example of the conventional optical pickup (PU) device. In FIG. 16, the reference numeral 131 represents a laser (LD), 132 a collimating lens (CL), 133 a beam shaping prism, 134 a beam splitter, 135 a deflecting prism, 136 a quarter-wave (λ/4) plate, 137 an objective lens, 138 an optical information recording medium, 139 a detection lens, 140 a knife-edge prism, 141 a light-receiving element for detecting the track, and 142 a light-receiving element for detecting the focus.
The light rays flux emitted from the semiconductor laser 131 is converted to parallel light rays by use of the collimating lens 132 and the beam of the light rays is enlarged by the beam shaping prism 133. In such manner, a preferable spot can be obtained on an optical information recording medium 138 mentioned later.
Thereafter, the light rays flux is radiated as an extremely small spot of almost 1 μm onto the optical information recording medium 138 after passing through the beam splitter 134, the deflecting prism 135, the quarter-wave plate (λ/4 plate) 136, and the objective lens 137. In such manner, the information is recorded and reproduced. The reflection right rays reflected on the optical information recording medium 138 pass through the objective lens 137, the quarter-wave plate (λ/4 plate) 136 and the deflecting prism 135, and the same are reflected on the beam splitter 134 and directed toward the detection system which comprises the detection lens 139, the knife-edge prism 140, the light receiving element 141 for detecting the track, and the light-receiving element 142 for detecting the focus.
FIG. 17a through 17c are diagrams showing the light-receiving element 142 for detecting the focus in FIG. 16. FIG. 17a shows the state in which the beam is located just at the center position between A and B, namely, the optimum state. FIG. 17b shows the state in which the beam is located at the B area, namely, the distant state.
FIG. 17c shows the state in which the beam is located at the A area, namely, the near state. As shown in FIGS. 17a through 17c, the focus detecting light-receiving element 142 is divided into two, A and B.
The amount and direction of the focus deviation is detected from the light intensity (amount) difference A−B of the light rays received by A and B, and the objective lens 137 is controlled in the direction of the arrow F shown in FIG. 16 such that the focus deviation becomes always not larger than 1 μm.
FIG. 18 shows a view showing a track detecting light-receiving element 141 in FIG. 16. As shown in FIG. 18, the track detecting light-receiving element 141 is divided into two, C and D. The spot focused by the objective lens 137 detects the amount and direction of the focus deviation from the light intensity (amount) difference C−D of the reflection light rays diffracted by a guide groove 143, and the objective lens 137 is controlled in the direction of the arrow T shown in FIG. 16 such that the track deviation becomes always not larger than 1 μm.
FIG. 19 is a view showing another example of the conventional optical pickup device (system) shown in FIG. 16. In FIG. 19, the reference numeral 144 represents an astigmatism generating element, and 145 a four-divisional light-receiving element. In the afore-mentioned FIG. 16, the knife-edge method is employed for detecting the focus. FIG. 19 shows an astigmatism method of employing the above-mentioned astigmatism generating element 144, and the four-divisional light-receiving element 145 is put on a circular position in which the light intensity distribution of the four-divisional elements; E, F, G, and H becomes almost uniform at the unfocused spot position. The track can be detected by the value: (E+G)−(F+H), in a similar way.
FIGS. 20a through 20c are diagrams showing the focusing state of the four-divisional light-receiving element in FIG. 19. FIG. 20a shows a proper (optimum) state. When the focus deviates, the spot of the light rays becomes elliptical as shown in FIGS. 20b and 20c. The amount and direction of the focus deviation can be judged by the shape of the elliptical spot. The track can be detected by the value: (E+F)−(G+H) as shown in FIG. 18.
The defect of the optical system in the conventional optical pickup device as mentioned before is that the number of the construction parts is large and the respective parts become large-sized. For this reason, the art shown in
document 2); Japanese Laid-open Patent Publication No. 4-87041/1992, employs a hologram and combines unitarily the semiconductor laser (LD) and the light-receiving element into one for the purpose of realizing a small-sized optical pickup.
FIG. 21 is a construction diagram showing the construction of the third example of the optical pickup device described in the above-mentioned
document 2), in which a hologram is employed, and the semiconductor laser and the light-receiving element are unitarily combined into one. In FIG. 21, the reference numeral 151 represents an objective lens, 152 a hologram plate, 153 a light-receiving element, 154 a laser diode (LD), 155 a light-receiving/emitting substrate, and 156 an optical disk.
The laser diode 154 and the light-receiving element 153 are mounted on the light-receiving/emitting substrate 155. The optical disk 156 and the optical pickup are in the positional relationship at the time of ordinary recording and reproducing. On this occasion, the outgoing light rays emitted from the laser diode 154 are focused on the recording/reproducing surface of the optical disk 156 by the hologram plate 152, and further, a part of the reflection light rays from the optical disk 156 is wave-surface-divided (diffracted) by the hologram of the hologram plate 152 and guided to the side of the light-receiving element 153. A part of the reflection light rays is focused on the central portion of the light-receiving element 153. On this occasion, a part of the light rays flux directed to the hologram plate 152 from the laser diode 154 is also wave-surface-divided by the hologram. However, since the wave-surface-divided light rays flux is reflected by the optical disk 156 in a direction opposite to that of the hologram plate 152, it does not exert any influence on the reproducing signal.
Nevertheless, the light utilizing efficiency is not so well. In general, the efficiency contributing to the spot is only a little less than 50% of the reflected light rays and the efficiency contributing to the detection system is only 10%-30% of the same. The above matter is a practical problem to be solved.
FIGS. 22a and 22b are perspective views respectively showing the construction of the fourth example of the conventional optical pickup device and the conventional hologram pickup device both described in the
document 3); Japanese Laid-open Patent Publication No. 5-120755/1993. In FIGS. 22a and 22b, the reference numeral 161 represents a disk, 162 an objective lens, 163 a collimating lens, 164 a beam splitter, 165 a grating, 166 a cover lens, 167 a laser diode (LD), 168 a photodevice, 169 a hologram, and 170 a hologram optical element (HOE).
The hologram optical element (HOE) 170 is made of a sheet of glass substrate. The hologram 169 is formed on the upper surface thereof, and a diffraction grating for creating the tracking beam is formed on the lower surface thereof. A plan plate beam splitter of the optical pickup, a light branch of concave lens, and a pickup control signal creating function are integrated in the hologram. The laser diode (LD) 167 and the photo-diode (FD) 168 for detecting the signal are mounted on a common stem and accommodated in one package. The hologram optical element 170 is bonded on the upper surface of the package with adhesive agents and unitarily combined with LD 167 and PD 168. In such construction, the number of the employed parts for constructing the pickup is reduced from 7 to 3. The package for LD 167 and PD 168 is hermetically sealed. In such manner, the positional relationship between the mutual elements can be kept extremely stable.
Next, the other actual examples of the conventional optical pickup device are described hereinafter.
As to the other conventional pickups, there exist four examples as mentioned below in order. Firstly, the construction of the fifth example of the conventional pickup device is explained referring to FIG. 40. The outgoing light rays emitted from a semiconductor laser 201 are converted to parallel light rays by a collimating lens 202. Thereafter, the converted light rays pass through a beam splitter 203 and the optical path of the light rays is bent by a deflecting prism 204. And further, the light rays are focused by an objective lens 205 and form a extremely small spot on the surface of an optical disk 206 employed as the optical information recording medium. Thereby, the recording, etc. of the information is done. Furthermore, the reflection light rays reflected on the optical disk 206 go forward in the direction opposite to that of the incident optical path and are reflected by the beam splitter 203. Next, the reflected light rays are focused by a detection lens 208 in a signal detecting optical system 207 and guided to a light-receiving element 209. Thereafter, the data information recorded on the surface of the optical disk 206 is reproduced, or the tracking servo control and the focusing servo control of the objective lens 205 are performed by detecting the track error signal and the focus error signal, on the basis of the distribution of the light amount (light intensity) detected by the light-receiving element 209.
Secondly, the construction of the sixth example of the conventional pickup device is explained referring to FIG. 41. The difference between the first example and the second example is that, in the second example, a magneto-optic disk 210 is employed as the optical information recording medium, and the construction in the signal detecting optical system 207 is changed. The polarizing surface of the reflection light rays reflected on the surface of the magneto-optic disk 210 is rotated by 45° by use of the half-wave (λ/2) plate 211 of the signal detecting optical system 207, and the light rays thus rotated are focused by the detection lens 208 and enter a polarizing beam splitter 212 as incident light rays. At this time, the P-polarized light rays pass through the polarizing beam splitter 212 and are guided to a light-receiving element 213. On the other hand, the S-polarized light rays are reflected on the polarizing splitter 212 and guided to the light-receiving element 214. Thereby, the data information on the surface of the magneto-optic disk 210 can be obtained as the differential signal between the signal from the light-receiving element 213 and that from the other light-receiving element 214.
Next, the construction of the seventh example of the conventional pickup device is explained referring to the disclosure in the
document, Japanese Laid-open Patent Publication No. 62-172538/1987, “Optical Head Apparatus”, and FIG. 42. In the example, a diffraction grating 215 is employed as the optical path separating measure in order to separate the foregoing light rays 216 emitted from the semiconductor laser 201 and directed to the optical disk 206 and the reflection light rays 217 reflected on the optical disk 206, from each other. Thereafter, the diffraction light rays 218 diffracted by a diffraction grating 215 among the reflection light rays 217 reflected on the optical disk 206 are guided to the light-receiving elements; 219a and 219b, which are disposed at the side of the semiconductor laser 201 and respectively have two-divisional light-receiving surfaces, and thereby the reproduction of the information signal can be done.
Finally, regarding the construction of the eighth example of the conventional pickup device, the assembling of the optical pickup apparatus construction is explained referring to FIG. 43. The semiconductor laser 201 is mounted on one end portion of an optical pickup housing 220, and an actuator base 221 is fixedly put on the bottom surface portion 220a thereof. A deflecting prism 222, an outer yoke 223, an inner yoke 224, and a magnet 225 are disposed on the actuator base 221. And further, a movable portion 226 of the actuator on which the objective lens 205 is supported is mounted on the upper portion of such actuator base 221. A focusing coil 227 and a tracking coil 228 are disposed on the side surface of the actuator's movable portion 226. On this occasion, when the electric current flows through the focusing coil 227, the actuator's movable portion 226 can be displaced in the focus direction F. On the other hand, when the electric current flows through the tracking coil 228, the actuator's movable portion 226 can be displaced in the tracking direction T.
In the fifth and sixth examples of the conventional pickup device construction (FIG. 40 and FIG. 41), the reflection light rays reflected on the optical disk 206 or the magneto-optic disk 210 are further reflected by the beam splitter 203, and thereby the reflection light rays can be separated from the outgoing light rays emitted from the semiconductor laser 201 and guided to the light-receiving elements; 209, 213, and 214 in the signal detecting optical system 207 in order to detect the signal. Since the signal detecting optical system 207 is separatedly provided in order to reproduce the signal in such manner, there arise several problems to be solved that the number of the optical parts employed is increased and that the space for the optical system is large-sized, and further, that the weight of the optical pickup portion is also increased and thereby the high-speed seeking operation cannot be performed.
In the seventh example of the conventional pickup device construction (FIG. 42), since there exists no signal detecting optical system 207 as mentioned above, it is possible to realize a small-sized and light-weight optical pickup portion. However, when the outgoing light rays emitted from the semiconductor laser 201 pass through the diffraction grating 215, diffused reflection light rays are generated on the grating surface thereof, and such diffused reflection light rays causes an undesirable phenomenon that the diffused reflection light rays enter the light-receiving elements; 219a and 219b, as flaring light rays. Since the signal level of the flaring light rays is equal to or more than the level of the signal component regularly (properly) detected by the light-receiving elements; 219a and 219b, there arises a problem to be solved that it is impossible to avoid the S/N-level-down of the properly detected signal.
In the eighth example of the conventional pickup device construction (FIG. 43), since the optical pickup portion is constructed such that the actuator base 221 is mounted on the optical pickup housing 220, and further, the actuator's movable portion 226 is mounted on the actuator base 221, the number of the assembled parts is large and therefore the number of the employed parts is increased. This is also a problem to be solved.